In recent years, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles that use fossil fuels.
Small-sized mobile devices use one or a few battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a battery module including a plurality of modularized battery cells or a battery pack including a plurality of battery modules electrically connected to each other, because high output and large capacity are necessary for such middle or large-sized devices.
Preferably, a middle or large-sized battery module or a middle or large-sized battery pack is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (i.e. a unit cell) of the middle or large-sized battery module or the middle or large-sized battery pack. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
Battery cells constituting the middle or large-sized battery module or the middle or large-sized battery pack are secondary batteries that can be charged and discharged. Consequently, a large amount of heat is generated from the high-output, large-capacity secondary batteries during the charge and discharge of the secondary batteries. In particular, the laminate sheet of a pouch-shaped battery cell has a polymer material exhibiting low thermal conductivity coated on the surface thereof, with the result that it is difficult to effectively lower the overall temperature of the battery cell.
If heat, generated from the battery cells during the charge and discharge of the battery cells, is not effectively removed from the battery cells, the heat accumulates in the battery cells, with the result that deterioration of the battery cells is accelerated. According to circumstances, the battery cells may even catch fire or explode. For this reason, a high-output, large-capacity battery module or a high-output, large-capacity battery pack needs a cooling system for cooling battery cells mounted in the battery module or the battery pack.
Meanwhile, at least one battery module mounted in a middle or large-sized battery pack is generally manufactured by stacking a plurality of battery cells with high integration. In this case, the battery cells are stacked in the state in which the battery cells are arranged at predetermined intervals such that heat, generated from the battery cells during the charge and discharge of the battery cells, is removed. For example, the battery cells may be sequentially stacked in the state in which the battery cells are arranged at predetermined intervals without using an additional member. Alternatively, in the case in which the battery cells have low mechanical strength, one or more battery cells may be mounted in a cartridge, and a plurality of cartridges may be stacked to constitute a battery module. In the above structure, refrigerant flow channels may be defined between the stacked battery cells or between the stacked battery modules such that heat accumulating between the stacked battery cells or between the stacked battery modules is effectively removed.
In the battery pack cooling structure described above, however, a plurality of refrigerant flow channels must be provided so as to correspond to a plurality of battery cells or battery modules, with the result that the overall size of the battery pack is increased.
In addition, if the battery pack includes a larger number of battery cells, a larger number of parts are added to the cooling structure, with the result that the volume of the battery pack is increased, the manufacturing process is complicated, and cost incurred to design the cooling structure is greatly increased.
Furthermore, a plurality of parts is used to constitute a structure in which heat from the battery modules or the battery cells is transferred to the refrigerant flow channels, by which the heat is removed, with the result that thermal conductivity is lowered and thus cooling efficiency is reduced.
Therefore, there is a high necessity for a cooling system that can be designed so as to have a compact structure while exhibiting high cooling efficiency.